A crop sprayer is used to distribute chemicals, such as herbicides, pesticides, and fertilizer, over crops in a field during a spraying operation. In order to maneuver the crop sprayer around the field during the spraying operation, an operator of the crop sprayer operates various controls which affect speed and direction of the crop sprayer. The speed and direction of the crop sprayer is directly related to the rotational speed and direction of a drive shaft of the crop sprayer.
Typically, one control allows the operator to selectively couple and decouple an engine crankshaft of the crop sprayer from the drive shaft. Another control allows the operator to selectively change the gear ratio between the engine crankshaft and the drive shaft. Still another control allows the operator to selectively increase and decrease rotational speed of the engine crankshaft.
By way of example, to control the movement of a conventional tractor, a foot activated clutch is used to selectively couple and decouple the engine crankshaft from the drive shaft, a hand actuated gear selector is used to selectively change the gear ratio between the engine crankshaft and the drive shaft, and a foot actuated throttle is used to control the rotational speed of the engine crankshaft.
In addition to the controls which the operator must operate in order to maneuver a crop sprayer around a field, the crop sprayer also includes other controls which operate the chemical spraying features of the crop sprayer. By way of example, the crop sprayer generally has a boom arm control which raises, lowers, extends, and retracts a boom arm which includes a number of spray nozzles. The crop sprayer further has a spray control which adjusts the flow rate of chemicals from a storage tank through the spray nozzles mounted on the boom arm.
Obviously, as the number of controls for various functions of a device increases, operation of the device becomes increasingly difficult. Moreover, coordinating operation of various controls, such as a clutch, a brake and the throttle, can be challenging, particularly when the controls are spatially separated.
One approach to reduce the burden on the operator of a crop sprayer is to utilize a hydrostatic drive system in the crop sprayer. A hydrostatic drive system includes a hand lever which when manipulated causes a hydraulic fluid to be advanced within the system so as to cause rotation of the wheels of the crop sprayer at a desired rotational speed and direction. Thus, use of the hydrostatic drive system eliminates the need for an operator to (i) use his foot to activate a clutch to selectively couple and decouple the engine crankshaft from the drive shaft, and (ii) to use his foot to selectively actuate the throttle to control the speed of the engine crankshaft. A separate control may be used to selectively change the gear ratio between the engine crankshaft and the drive shaft. Consequently, the use of a hydrostatic drive system enables an operator to maneuver the crop sprayer around the field with a fewer number of separate controls thereby reducing the burden on the operator of the crop sprayer.
One drawback of a hydrostatic drive system is that hydrostatic drive systems are typically heavy, complex, and expensive. The weight of a hydrostatic drive system inhibits mobility of a crop sprayer, especially in soft terrain. Wider tires can be used to distribute the weight of the crop sprayer over a larger area so as to increase mobility. The use of wider tires, however, requires an additional distance to be provided between adjacent rows of the crop in order to ensure that the crops being sprayed are not damaged by the tires during a spraying operation. This reduces the number of crops that may be planted for a given area. Alternatively, an operator may choose to maintain the same row separation resulting in a reduced clearance between the tires and the crops. Maintaining the wheels within a relatively narrow space, however, increases the required level of concentration and increases the amount of tension and fatigue experienced by an operator.
What is needed therefore is an apparatus and method for reducing the number of separate controls required to control the movement and operation of a crop sprayer without significantly increasing the weight of the crop sprayer.